Interleukin-5 (hereinafter referred to a "IL-5") is a kind of lymphokine which is secreted by T cells, mast cells and other cells. Murine IL-5 is known to act as a differentiation and growth factor for B cells and eosinophils. Human IL-5 is known to act mainly as a differentiation and growth factor for eosinophils (Advances in Immunology, 57, 145 (1994); Blood, 79, 3101 (1992)). IL-5 exhibits its action through a specific receptor (IL-5 receptor) which is expressed on the surface of a cell such as eosinophil. It has been shown that human and murine IL-5 receptors (hereinafter referred to as "IL-5Rs") are both composed of two different kinds of proteins, an .alpha. chain (hereinafter referred to as "IL-5R.alpha.") and a .beta. chain (hereinafter referred to as "IL-5R.beta."). In addition, it is known that the binding of IL-5 to IL-5R is via IL-5R.alpha. and that IL-5R.beta. alone can not bind to IL-5 (EMBO J., 9, 4367 (1990); ibid., 10, 2833 (1991); J. Exp. Med., 177, 1523 (1993); ibid., 175, 341 (1992); Cell, 66, 1175 (1991), Proc. Natl. Acad. Sci., 89, 7041 (1992)). Furthermore, IL-5R.beta. is known to be a component of receptors for interleukin-3 (hereinafter referred to as "IL-3"), granulocyte macrophage colony-stimulating factor and others (hereinafter referred to as "GM-CSF") (Proc. Natl. Acad. Sci., 87, 9655 (1990); Cell, 66, 1165 (1991)).
Eosinophils are known to increase in allergic diseases represented by chronic bronchial asthma. Significant infiltration of eosinophils is observed in airways of a patient with chronic bronchial asthma. Eosinophil contains a cytotoxic granular proteins whose deposit is observed in airway tissues of a patient with chronic bronchial asthma or at lesion sites of a patient with atopic dermatitis. These facts suggest that eosinophil plays an important role in the pathogenesis of allergic disorders such as chronic bronchial asthma, atopic dermatitis and the like (Adv. Immunol., 39, 177 (1986); Immunol. Today, 13, 501 (1992)). Hence, studying the kinetics of eosinophils is useful for clinical diagnosis. On the other hand, human IL-5 acts specifically on eosinophils, so IL-5R is believed to be expressed specifically in eosinophils and can therefore be used as a marker specific to human eosinophils. Furthermore, IL-5.beta. is a receptor for cytokines such as IL-3, GM-CSF and others, so IL-5R.alpha. is believed to be a marker specific to eosinophils. Hence, eosinophils can be detected specifically by immunocyte staining using an anti-human IL-5R.alpha. chain antibody (hereinafter referred to as "anti-hIL-5R.alpha. antibody"). However, no anti-hIL-5R.alpha. antibody is presently known that is capable of specific detection of eosinophils.
Significant eosinophilia was observed in IL-5 transgenic mice (J. Exp. Med., 172, 1425 (1990); ibid. 173, 429 (1991); Int. Immunol., 2, 965 (1990)). Eosinophil infiltration in tissues was suppressed by the administration of an anti-IL-5 antibody in animal models of asthma (Am. Rev. Resir. 147, 548 (1993); ibid., 148, 1623 (1993)). These phenomena indicate that IL-5 actually plays an important role in eosinophilia and the infiltration of eosinophils in vivo. It is also reported that IL-5 is expressed in airway mucosal tissues of a human patient with chronic bronchial asthma and at lesion sites of a patient with atopic dermatitis (J. Clin. Invest., 87, 1541 (1991); J. Exp. Med., 173, 775 (1991)). Further investigations demonstrate that IL-5 exhibits in vitro viability-enhancing action on human eosinophils (J. Immunol., 143, 2311 (1989)) and that IL-5 is an eosinophil-selective activator (J. Exp. Med.,167, 219 (1988)).
Hence, antibodies that bind to IL-5R and which can inhibit the biological activity of IL-5 are expected to inhibit the activity of eosinophil, thus being useful in the treatment of allergic diseases such as chronic bronchial asthma. Anti-mouse IL-5R.alpha. antibodies which can inhibit the biological activity of IL-5 were produced by using as an antigen those IL-5-dependent cells which express a large number of murine IL-5R on their surfaces (Kokai (Japanese published unexamined patent application) No. 108497/91; Int. Immunol., 2, 181 (1990)). However, in the case of humans, no cells are known which express a large number of IL-5R and the expression of IL-5R is reported to be very low in eosinophils (Cell.
Immunol., 133, 484 (1991)). Hence, anti-human IL-5R.alpha. antibodies having comparable functions to anti-mouse IL-5R.alpha. antibodies are difficult to produce by methods similar to those for producing the latter. An antibody designated as ".alpha.16"is disclosed as an antibody against human IL-5R.alpha. in EMBO J., 14, 3395 (1995) but this antibody does not have any neutralization activity for IL-5R.alpha..
Human IL-5R.alpha. gene was obtained by preparing a cDNA library from human eosinophil (J. Exp. Med., 175, 341 (1992)) or a human promyelocytic cell HL-60 (Cell, 66, 1175 (1991); Kokai No. 78772/94) and screening the library using as a probe an oligo DNA which had been synthesized on the basis of cDNA of murine IL-5R.alpha. or a partial amino acid sequence of murine IL-5R.alpha. (Kokai No. 54690/94, EMBO J., 9, 4367 (1990)). The transfer of the cDNA into a host cell resulted in the creation of a cell having hIL-5R.alpha. expressed on its surface but the expression level of hIL-5R in this cell was very low (.ltoreq.10.sup.4 molecules) (J.
Exp. Med., 177, 1523 (1993)). Hence, if one attempts to produce anti-hIL-5R.alpha. antibodies by using this cell as an immunogen, he will find that the relative amount of hIL-5R.alpha. is very small, compared with those of proteins from a host cell and that the absolute protein amount of hIL-5R.alpha. is also very small. In addition, approximately 80% homology at an amino acid level is observed between murine IL-5R.alpha. and human IL-5R.alpha. and murine IL-5 can bind to human IL-5R with high affinity (J. Exp. Med., 175, 341 (1992)). These facts suggest that human IL-5R.alpha. has a lower immunogenicity for mice or rats which are commonly used as animals to be immunized. In fact, almost all of our attempts to prepare anti-hIL-5R.alpha. antibodies using hIL-5R.alpha.-expressing cells as an immunogen resulted in a failure.
In the cloning of IL-5R cDNA from a cDNA library of human eosinophil, cDNA encoding soluble human IL-5R.alpha. (hereinafter referred to as "shIL-5R.alpha.") has been obtained which corresponds to the N-terminal amino acid sequence (1-313) of IL-5R.alpha. which is defective in the transmembrane region and onwards (J. Exp. Med.,175, 341 (1992)). When shIL-5R.alpha. is used as an immunogen to produce an anti-hIL-5R.alpha. antibody, the shIL-5R.alpha. should have the same three dimensional conformation as that of IL-5R.alpha. expressed on the cell surface and it should be one secreted and produced by a eukaryotic host cell in order to obtain an anti-hIL-5R.alpha. antibody which can inhibit the biological activity of IL-5. In addition, it has been found that the production efficiency of a protein varies significantly depending on the signal peptide (Protein, Nucleic Acid and Enzyme, 35, 2584 (1990)), so it is necessary to select an appropriate signal peptide for secretion and production of the protein.
As mentioned above, it has been found that mRNA which is believed to encode only shIL-5R.alpha. is expressed in eosinophils. It has been confirmed that murine IL-5R is expressed not only in eosinophils but also in B cells and that mRNA which is believed to encode only an extracellular region of IL-5R.alpha. (hereinafter referred to as "smIL-5R.alpha.") is expressed in those cells as well as in the case of humans. In addition, it has been reported that smIL-5R.alpha. was detected in blood of mice transplanted with IL-5R expressing murine chronic B cell leukemia cell line (BCL1) or model mice of human autoimmune diseases (J. Immunol. Method, 167, 289 (1994)). These suggest the possibility that the increase in the number of IL-5R expressing cells and their activation may be reflected in the amount of smIL-5R.alpha. secreted in blood. Human IL-5R is believed to be expressed in eosinophils in a limited amount and the increase in the number of eosinophils and their activation may be potentially reflected in the amount of shIL-5R.alpha. in blood. Hence, the quantitative determination of shIL-5R.alpha. is expected to be useful in clinical diagnosis.
Any isolated monoclonal antibody which binds specifically to human IL-5R.alpha. is believed to be useful in the diagnosis and treatment of allergic diseases. However, it should be noted that if a non-human animal-derived monoclonal antibody is administered to a human, it is generally recognized as a foreign matter such that an antibody against the non-human animal-derived monoclonal antibody is produced in the human body, a reaction with the administered non-human animal-derived monoclonal antibody occurs to cause a side effect (J. Clin. Oncol., 2, 881 (1984); Blood, 65, 1349 (1985); J. Natl. Cancer Inst., 80, 932 (1988); Proc. Natl. Acad. Sci., 82, 1242 (1985)), premature clearance of the non-human animal-derived monoclonal antibody occurs (J. Nucl. Med.,26, 1011 (1985); Blood, 65, 1349 (1985); J. Natl. Cancer Inst., 80, 937 (1988)), or therapeutic effect of the monoclonal antibody is reduced (J. Immunol.,135, 1530 (1985); Cancer Res., 46, 6489 (1986)).
In order to solve these problems, attempts have been made to convert non-human animal-derived monoclonal antibodies to human chimeric antibodies or human CDR-grafted antibodies (reconstituted human antibodies) by gene recombinant techniques. A human chimeric antibody is an antibody of which the variable region (hereinafter referred to as "V region") is derived from a non-human animal antibody and the constant region (hereinafter referred to as "C region") is derived from a human antibody (Proc. Natl. Acad. Sci., 81, 6851 (1984)). It has been reported that when a human chimeric antibody is administered to a human, antibodies are hardly produced against the non-human animal-derived monoclonal antibody and a half-life in blood is increased by a factor of 6 (Proc. Natl. Acad. Sci.,86, 4220 (1989)). A human CDR-grafted antibody is a human antibody of which the CDR (complementarity determining region) is replaced with the CDR of a non-human animal-derived antibody (Nature, 321, 522 (1986)). It has been reported with experiments on monkeys that a human CDR-grafted antibody has a lower immunogenicity, with the half-life in blood being increased by a factor of 4-5 compared with a mouse antibody (J. Immunol.,147, 1352 (1991)). However, there is no report about a humanized antibody against hIL-5R.alpha..
When a humanized antibody which binds specifically to human IL-5R.alpha. is administered to a human, it is expected to cause no production of an antibody against a non-human animal-derived monoclonal antibody, thereby reducing the side effect and prolonging the half-life in blood, which eventually leads to a high therapeutic effect against allergic diseases such as chronic bronchial asthma, atopic dermatitis and the like.
As a result of the recent progresses in protein and genetic engineering, smaller antibody molecules such as single chain antibodies (Science, 242, 423 (1988)) and disulfide stabilized antibodies (Molecular Immunology, 32, 249 (1995)) are being prepared. Since single chain antibodies and disulfide stabilized antibodies have smaller molecular weights than monoclonal antibodies and humanized antibodies, they are effective in transition into tissues and clearance from blood and their application to the imaging technology and the preparation of complexes with toxins are being underway to provide some promise in therapeutic efficacy (Cancer Research, 55, 318 (1995)). If a single chain antibody or a disulfide stabilized antibody which binds specifically to a human IL-5R.alpha. chain is produced, high diagnostic and therapeutic effects against allergic diseases and the like are anticipated. However, there is no report about a single chain antibody and a disulfide stabilized antibody against a human IL-5R.alpha. chain.